Aci 318-08, Appendix D
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ACI 318-08, Appendix D IBC 2006 Section 1912 Anchorage to Concrete Mark Bartlett, PE Field Engineer Simpson Anchor Systems
Presentation Topics
• •
Brief History of Anchor Design ACI 318-08, Appendix D • • • • • • •
• • • •
Design Equations Phi (Ф) Factors Interaction Equation Seismic Provisions Reinforcement to Prevent Breakout Other Issues Edge Distances, Thicknesses & Spacings
When to design per App. D IBC 2006 Adhesive Anchors and Concrete Screws The Future of Anchor Design
1
Prior to ACI 318-02
• Cast-In-Place anchors covered by: – PCI / ACI 349 – UBC / IBC codes listed allowable stress capacities for CIP bolts
Prior to ACI 318-02
• Design of Post-Installed anchors: – Individual manufacturers supplied load values based on testing – Values found in catalogs and ICBO/ICC reports – Methodology was allowable stress and assumed an uncracked and unreinforced section.
2
ACI 318-08, Appendix D
ACI 318, Appendix D
• Strength design method for anchorage to concrete (i.e. Nua ≤ ΦNn or Vua ≤ ΦVn) – Cast-In-Place (CIP) anchors – Post-Installed (PI) anchors
• Undercut anchors • Torque-controlled anchors • Deformation-controlled anchors
– PI anchors must be prequalified per ACI 355.2
3
Appendix D Design Equations & Failure Modes
• Design equations check 5 different failure modes – Steel capacity • Tension and Shear
– Concrete breakout capacity • Tension and Shear
– Pullout/Pull-through capacity • Tension only
– Concrete Pryout • Shear only
– Concrete side-face blowout • Tension and CIP only.
Appendix D Design Equations
4
Design Equations
Tension Capacities Nsa = nAse,Nfuta Ncb = ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Npn = Ψc,PNp Nsb = (160ca1√Abrg)λ√f’c Shear Capacities Vsa = n 0.6 Ase,V futa Vcbg = AVc/AVco(Ψec,VΨed,V Ψc,V Ψh,VVb) Vcpg = kcpNcbg
Steel Strength in Tension
5
Steel Strength In Tension – D.5.1
Nsa = nAse,Nfuta (Eq. D-3)
– Nsa – Nominal tensile strength of an anchor group – n – Number of anchors – Ase,N – Effective cross sectional area of anchor in tension – futa – Specific ultimate tensile strength of anchor
Concrete Breakout Strength in Tension
6
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) (Eq. D-5)
• Ncb – Concrete breakout strength in tension
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) • ANc – Projected failure area of group • ANco = 9 hef2 Projected failure area of one anchor (Eq. D-6)
7
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Modification for eccentric load Ψec,N = 1/[1+(2e’N/3hef)] (Eq. D-9) N Centroid of anchors
T3
T2
e’N
T1
Resultant tension load
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Modification for edge effects
If ca,min > 1.5hef then: Eq. D-10 Ψed,N = 1.0
ca
If ca,min < 1.5hef then: Eq. D-11 Ψed,N = 0.7 + 0.3 (ca,min / 1.5hef )
8
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Modification for cracking Ψc,N =1.4 for uncracked section if kc = 17 in eq. (D-7) Ψc,N per evaluation report (ER) if kc from ER used in eq. (D-7) Ψc,N =1.0 for cracked section
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,NΨc,NΨcp,NNb) Ψcp,N – Modification for Post-Installed anchors Uncracked concrete No supplemental reinf. to control splitting
If ca,min > cac then: Ψcp,N = 1.0 (Eq. D-12) If ca,min < cac then: Ψcp,N = ca,min/cac (Eq. D-13) Where cac= 2.5 hef (undercut anchors) 4 hef (wedge anchors)
9
Concrete Breakout In Tension – D.5.2
Ncbg=ANc/ANco(Ψec,NΨed,NΨc,NΨcp,NNb) • Basic concrete breakout strength • Nb=kc λ √f’c hef1.5 (Eq. D-7) – kc – Coefficient for basic concrete breakout strength
• Found in either App. D or per product ER
– λ – Modification factor for lightweight concrete – f’c – Concrete compressive strength – hef – Effective embedment depth
• Tested hef found in manufacturer’s catalog or product ER
Pullout Strength in Tension
10
Pullout Strength In Tension – D.5.3
Npn = Ψc,PNp
(Eq. D-14)
• Npn – Nominal pullout strength • Ψc,P – Modification for cracking – 1.0 for cracked – 1.4 for uncracked
• Np – Pullout strength in tension
Pullout Strength In Tension – D.5.3
Npn = Ψc,P Np
(Eq. D-14)
• Np – Pullout strength in tension • For PI anchors Np based on ACI 355.2 test results • For CIP anchors, Np based on: – Np = 8 Abrgf’c (Eq. D-15) headed bolts – Np = 0.9f’cehda (Eq. D-16) hooked bolts
11
Side-Face Blowout Strength in Tension
Side-Face Blowout Strength – D.5.4
Nsb = (160ca1√Abrg)λ√f’c (Eq. D-17) • Nsb – Side-face blowout strength (headed anchors only) • ca1 – edge distance • Abrg – Net bearing area of the head of anchor • λ – Modification factor for lightweight concrete
12
Steel Strength in Shear
Steel Strength In Shear – D.6.1
• Vsa = n Ase,V futa (eq. D-19) CIP HSA • Vsa = n 0.6 Ase,V futa (eq. D-20) – n – number of anchors – Ase,V – effective cross sectional area of a single anchor in shear – futa – specified tensile strength of anchor steel
13
Steel Strength In Shear – D.6.1
• Vsa may also be based on the results of tests performed and evaluated according to ACI 355.2
Concrete Breakout Strength in Shear
14
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,V Ψc,V Ψh,VVb) (Eq. D-22)
• Vcbg – Concrete breakout strength in shear
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) – AVc – projected concrete failure area of a group of anchors c
a1
V
ha 1.5ca1
s1
ca2
AVc
AVc = (1.5ca1 + s1 + ca2) ha
15
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) – AVco – maximum projected concrete failure area of a single anchor
V
c
a1
AVco = 4.5 ca12 (Eq. D-23)
1.5c1 1.5ca1 1.5ca1
AVco
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψec,V – Modification for eccentric load (Eq. D-26)
16
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψed,V – Modification for edge effects If ca2 > 1.5ca1 then Ψed,V = 1.0 (Eq. D-27)
V
If ca2 < 1.5ca1 then Ψed,V = 0.7 + 0.3ca2/1.5ca1
ca1
(Eq. D-28)
ca2
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V Modification factor for cracking Ψc,V = 1.4 for anchors located in a region where analysis indicates no cracking at service loads Who is currently doing this analysis?
17
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V = 1.0 for anchors in cracked concrete with no supplemental reinforcement or edge reinforcement smaller V than a #4 bar <#4
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V = 1.2 for anchors in cracked concrete with reinforcement of a #4 bar or greater between the anchor and the edge V
>#4
18
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V = 1.4 for anchors in cracked concrete with reinforcement of a #4 bar or greater between the anchor and the edge, and with the reinforcement enclosed V within stirrups spaced at not more than 4”.
≥#4 #4@4”
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψh,V – Modification factor for shear strength of anchors located in concrete members with ha < 1.5ca1
c
When ha < 1.5ca1, AVc is reduced. However, breakout strength is not directly proportional to member thickness. Ψh,V adjusts for this.
a1
Ψh,V = √1.5ca1/ha but not less than 1.0
1.5c1
V
ha
19
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) • Vb=(7(ℓe /da)0.2√da)λ√f’c (ca1)1.5
(Eq. D-24)
– ℓe – load bearing length of anchor • Same as hef if there is no sleeve on anchor • Per manufacturer if there is a sleeve
– da – outside diameter of anchor – λ – adjustment for lightweight concrete – f’c – concrete compressive strength – ca1 – edge distance
Pryout Strength in Shear
20
Concrete Pryout Strength In Shear – D.6.3
Vcpg = kcpNcbg
(Eq. D-30)
• •
kcp = 1.0 for hef < 2.5” kcp = 2.0 for hef > 2.5”
•
Ncbg – Nominal concrete breakout strength in tension – Always do tension calcs first
Phi (Ф) Factors
21
Phi (Φ) factors
• Nua ≤ ΦNn or Vua ≤ ΦVn • Phi (Ф) factors are applied to nominal capacities before comparing with factored forces • Based on: – Supplemental reinforcement – Failure mode – Load type – Anchor property
Phi (Φ) factors D.4.4 Ф Factor Failure Mode
Anchor Property
Condition A Tension
Condition B
Shear
Ductile Steel
Shear
0.75
0.65
0.65
0.60
Use Condition B Brittle
Side Face Blowout
Tension
CIP
0.75
0.75
0.70
0.70
CIP
0.75
0.75
0.70
0.70
Cat. 1
0.75
0.75
0.65
0.70
Cat. 2
0.65
0.75
0.55
0.70
Cat. 3
0.55
0.75
0.45
0.70
0.70
0.70
Breakout
CIP Cat. 1
0.65
0.70
Cat. 2
0.55
0.70
Cat. 3
0.45
0.70
CIP
0.70
0.70
Pullout
Use Condition B
Cat. 1
0.65
0.70
Cat. 2
0.55
0.70
Cat. 3
0.45
0.70
Pryout
Use Condition B
22
Supplemental Reinforcing D.4.4 • Condition A – Applies where supplementary reinforcement is present except for pullout and pryout strengths. • Condition B – Applies where supplementary reinforcement is not present, and for pullout or pryout strength.
Supplemental Reinforcing
• Supplemental Reinforcement – Reinforcement that acts to restrain the potential concrete breakout but is not designed to transfer the full design load from the anchors into the structural member. – Refer to sections D.5.2.9 and D.6.2.9 for full design load transfer requirements
23
Interaction of Tension and Shear
Interaction of Tension and Shear – D.7
24
Interaction of Tension and Shear – D.7
• If Vua≤0.2ΦVn full tension allowed – Ignore Shear
• If Nua≤0.2ΦNn full shear allowed – Ignore Tension
• Otherwise Nua + Vua ΦNn ΦVn
< 1.2
Appendix D Seismic Provisions
25
Seismic Provisions
D.3.3 – When anchor design includes earthquake forces for structures assigned to Seismic Design Category C, D, E, or F, the additional requirements of D.3.3.1 through D.3.3.6 shall apply.
D.3.3.1 – The provisions of Appendix D do not apply to the design of anchors in plastic hinge zones of concrete structures under earthquake forces.
D.3.3.2 – Post-installed structural anchors shall be qualified for use in cracked concrete and shall have passed the Simulated Seismic Tests in accordance with ACI 355.2. Pullout strength Np and steel strength of the anchor in shear Vsa shall be based on the results of the ACI 355.2 Simulated Seismic Tests.
Seismic Provisions D.3.3.3 – The anchor design strength associated with concrete failure modes shall be taken as 0.75φNn and 0.75φVn, where φ is given in D.4.4 or D.4.5, and Nn and Vn are determined in accordance with D.5.2, D.5.3, D.5.4, D.6.2, and D.6.3, assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked.
• 0.75 reduction to concrete capacity in Seismic Design Category C – F • Impractical to prove concrete remains uncracked
26
Seismic Provisions
D.3.3.4 – Anchors shall be designed to be governed by the steel strength of a ductile steel element as determined in accordance with D.5.1 and D.6.1, unless either D.3.3.5 or D.3.3.6 is satisfied. D.3.3.5 – Instead of D.3.3.4, the attachment that the anchor is connecting to the structure shall be designed so that the attachment will undergo ductile yielding at a force level corresponding to anchor forces no greater than the design strength of anchors specified in D.3.3.3. D.3.3.6 – As an alternative to D.3.3.4 and D.3.3.5, it shall be permitted to take the design strength of the anchors as 0.4 times the design strength determined in accordance with D.3.3.3. For the anchors of stud bearing walls, it shall be permitted to take the design strength of the anchors as 0.5 times the design strength determined in accordance with D.3.3.3.
Seismic Provisions
• Summary – Seismic Design Category C, D, E & F – No anchors in plastic hinge – PI anchors must pass Simulated Seismic Test – Design strength reduced by 25% – Ductile steel failure of anchors shall control, or... – Ductile yielding of attachment, or... – Anchor capacity reduced by 60%
27
Seismic Provisions
• Seismic and edge effects – At small edge distances, concrete breakout (non ductile failure mode) will often control – If attachment will not experience ductile yielding before breakout occurs, then 40% anchor capacity reduction unless... – Reinforce section to prevent breakout from occurring
Reinforcement to Prevent Concrete Breakout
28
Reinforcement to Prevent Concrete Breakout D.4.2.1 – The effect of reinforcement provided to restrain the concrete breakout shall be permitted to be included in the design models used to satisfy D.4.2. Where anchor reinforcement is provided in accordance with D.5.2.9 and D.6.2.9, calculation of the concrete breakout strength in accordance with D.5.2 and D.6.2 is not required.
D.5.2.9 – Where anchor reinforcement is developed in accordance with Chapter 12 on both sides of the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining φNn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
Reinforcement to Prevent Concrete Breakout
• Refer to Commentary RD.5.2.9 for more information
29
Reinforcement to Prevent Concrete Breakout D.6.2.9 – Where anchor reinforcement is either developed in accordance with Chapter 12 on both sides of the breakout surface, or encloses the anchor and is developed beyond the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining φVn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
Plan
Section
• Refer to Commentary RD.6.2.9 for more info
Bars effective as anchor reinforcement
Reinforcement to Prevent Concrete Breakout
Edge Reinforcement Anchor Reinforcement
Section
Plan
• Refer to Commentary RD.6.2.9 for more info
30
Reinforcement to Prevent Concrete Breakout
• Per Commentary RD.5.2.9 and RD.6.2.9: – “As a practical matter, use of anchor reinforcement is generally limited to cast-in-place anchors.”
• What about post-installed anchors? – At small edge distances, anchor capacity will be greatly reduced for seismic design.
Other Appendix D Issues
31
Capacity Adjustments • PI anchor pullout capacity – Tested values of Np are done in 2500 psi concrete – Pullout capacities increase for higher f’c – Adjustment equations in ER
• Grout pads – 20% reduction in shear strength (D.6.1.3) – App. D makes no mention to grout pad thickness
• Shear load parallel to concrete edge – Breakout capacity doubled per D.6.2.1(c).
Triple Edge Conditions
D.5.2.3 – Where anchors are located less than 1.5hef from three or more edges, the value of hef used in Eq. (D-4) through (D-11) shall be the greater of ca,max/1.5 and one-third of the maximum spacing between the anchors within the group.
D.6.2.4 – Where anchors are influenced by three or more edges, the value of ca1 used in Eq. (D-23) through (D-29) shall be the greatest of ca2/1.5 in either direction, ha/1.5; and one-third of the maximum spacing between the anchors within the group.
32
Triple Edge Condition in Tension
Triple Edge Condition in Shear
33
Corner Condition D.6.2.1(d)
(d) For anchors located at a corner, the limiting nominal concrete breakout strength shall be determined for each edge, and the minimum value shall be used.
V V ca1
ca2 ca2
ca1
Shear Near an Edge D.6.2.1 Where anchors are located at varying distances from the edge and the anchors are welded to the attachment so as to distribute the force to all anchors, it shall be permitted to evaluate the strength based on the distance to the farthest row of anchors from the edge. In this case, it shall be permitted to base the value of ca1 on the distance from the edge to the axis of the farthest anchor row that is selected as critical, and all of the shear shall be assumed to be carried by this critical anchor row alone.
Anchors welded to plate
V
0.5V
Anchors not welded to plate
0.5V
ca1 ca1
34
Shear Near an Edge D.6.2.1
• Increase ca1 without welding to plate – Slot holes closest to edge
V ca1
Required Edge Distances, Spacings, and Thicknesses
35
Section D.8
Minimum spacings and edge distances for anchors and minimum thicknesses of members shall conform to D.8.1 through D.8.6, unless supplementary reinforcement is provided to control splitting. Lesser values from product-specific tests performed in accordance with ACI 355.2 shall be permitted. D.8.1 – Unless determined in accordance with D.8.4, minimum center-to-center spacing of anchors shall be 4da for untorqued cast-in anchors, and 6da for torqued cast-in anchors and post-installed anchors. D.8.2 – Unless determined in accordance with D.8.4, minimum edge distances for cast-in headed anchors that will not be torqued shall be based on specified cover requirements for reinforcement in 7.7. For castin headed anchors that will be torqued, the minimum edge distances shall be 6da.
Section D.8
D.8.3 – Unless determined in accordance with D.8.4, minimum edge distances for post-installed anchors shall be based on the greater of specified cover requirements for reinforcement in 7.7, or minimum edge distance requirements for the products as determined by tests in accordance with ACI 355.2, and shall not be less than 2.0 times the maximum aggregate size. In the absence of product-specific ACI 355.2 test information, the minimum edge distance shall be taken as not less than: Undercut anchors..................................................6da Torque-controlled anchors.....................................8da Displacement-controlled anchors.........................10da
36
Section D.8
D.8.4 – For anchors where installation does not produce a splitting force and that will remain untorqued, if the edge distance or spacing is less than those specified in D.8.1 to D.8.3, calculations shall be performed by substituting for da a smaller value d’a that meets the requirements of D.8.1 to D.8.3. Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of d’a. D.8.5 – The value of hef for an expansion or undercut post-installed anchor shall not exceed the greater of 2/3 of the member thickness and the member thickness minus 4 in.
Section D.8
D.8.6 – Unless determined from tension tests in accordance with ACI 355.2, the critical edge distance, cac, shall not be taken less than: Undercut anchors...............................................2.5hef Torque-controlled anchors....................................4hef Displacement-controlled anchors..........................4hef
37
Limitations of Appendix D
• Applies for CIP and some PostInstalled anchors – Specialty inserts, through bolts, adhesive anchors, screw anchors, PAT fasteners outside scope of Appendix D – ACI Commentary: “Adhesive anchors are widely used and can perform adequately. At this time…outside the scope.”
Limitations of Appendix D
• NW Concrete and LW Concrete only – Reductions in capacity in LW – CMU and Concrete on metal deck outside scope of App. D • Grouted CMU will still use existing postinstalled anchor products
38
Limitations of Appendix D
• Limits to: – Diameter (≤2”) – Embedment depth (≤25”) – Concrete compressive strength (≤8000 psi PI; <10000 psi CIP).
When to Use Appendix D
39
When to use Appendix D
• Per ACI 318-08, D.2.1 – “…anchors in concrete used to transmit structural loads by means of tension, shear, or a combination of tension and shear between (a) connected structural elements; or (b) safety-related attachments and structural elements.” – What is a “safety-related attachment”?
When to use Appendix D
• Per ACI 318-08, RD.2.1 – Commentary lists examples for safetyrelated attachments. – “…safety-related attachments that are not part of the structure (such as sprinkler systems, heavy suspended pipes, or barrier rails) are attached to structural elements.” – Will sprinkler systems be attached with cracked concrete anchors?
40
When to Use Appendix D IBC 2006
IBC 2006, Section 1911
Anchorage To Concrete – Allowable Stress Design 1911.1 Scope. The provisions of this section shall govern the allowable stress design of headed bolts, and headed stud anchors cast in normal-weight concrete for purposes of transmitting structural loads from one connected element to the other. These provisions do not apply to anchors installed in hardened concrete or where load combinations include earthquake loads or effects. The bearing area of headed anchors shall be not less than one and one-half times the shank area. Where strength design is used, or where load combinations include earthquake loads or effects, the design strength of anchors shall be determined in accordance with Section 1912. Bolts shall conform to ASTM A 307 or an approved equivalent.
41
IBC 2006, Section 1912 Anchorage To Concrete – Strength Design 1912.1 Scope. The provisions of this section shall govern the strength design of anchors installed in concrete for purposes of transmitting structural loads from one connected element to the other. Headed bolts, headed studs and hooked (J- or L-) bolts cast in concrete and expansion anchors and undercut anchors installed in hardened concrete shall be designed in accordance with Appendix D of ACI 318 as modified by Section 1908.1.16, provided they are within the scope of Appendix D. Exception: Where the basic concrete breakout strength in tension of a single anchor, Nb, is determined in accordance with Equation (D-7), the concrete breakout strength requirements of Section D.4.2.2 shall be considered satisfied by the design procedures of Sections D.5.2 and D.6.2 for anchors exceeding 2 inches (51mm) in diameter or 25 inches (635mm) tensile embedment depth. The strength design of anchors that are not within the scope of Appendix D of ACI 318, and as amended above, shall be in accordance with an approved procedure.
IBC 2006, Section 1908 Modifications to ACI 318 1908.1.16 ACI 318, Section D.3.3. Modify ACI 318, section D.3.3.2 through C.3.3.5, to read as follows: D.3.3.2 – In structures assigned to Seismic Design Category C, D, E or F, post-installed anchors for use under D.2.3 shall have passed the Simulated Seismic Tests of ACI 355.2. D.3.3.3 – In structures assigned to Seismic Design Category C, D, E or F, the design strength of anchors shall be taken as 0.75φNn and 0.75φVn, where φ is given in D.4.4 or D.4.5, and Nn and Vn are determined in accordance with D.4.1. D.3.3.4 – In structures assigned to Seismic Design Category C, D, E or F, anchors shall be designed to be governed by tensile or shear strength of a ductile steel element, unless D.3.3.5 is satisfied. D.3.3.5 – Instead of D.3.3.4, the attachment that the anchor is connecting to the structure shall be designed so that the attachment will undergo ductile yielding at a load level corresponding to anchor forces no greater than the design strength of anchors specified in D.3.3.3, or the minimum design strength of the anchors shall be at least 2.5 times the factored forces transmitted by the attachment.
42
Adhesive Anchors and Concrete Screws
Adhesives Anchors and Concrete Screws
• IBC 2006, Section 1912 – “The strength design of anchors that do not within the scope of Appendix D of ACI 318…shall be in accordance with an approved design procedure.”
• What design procedures are approved? • Who decides?
43
Adhesives Anchors and Concrete Screws
• IBC 2006, Section 104.11 104.11 Alternative materials, design and methods of construction and equipment. The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. 104.11.1 Research reports. Supporting data, where necessary to assist in the approval of materials or assemblies not specifically provided for in this code, shall consist of valid research reports from approved sources.
Adhesives Anchors and Concrete Screws
• IBC 2006, Section 104.11 – The building official has the ability to approve a material if it is not specifically referenced in the code – Adhesive anchors and screw anchors fall into this category – Caution: Most building officials are still learning about strength design provisions of anchors
44
Adhesives Anchors and Concrete Screws
• Many engineers are still designing adhesive anchors and screw anchors per ASD • Strength design code reports for adhesives and screws are just starting to come online
Adhesives Anchors and Concrete Screws
• ICC ES AC 193 – Expansion anchors – Undercut anchors – Screw anchors
• ICC ES AC 308 – Adhesive anchors
45
Code Reports
The Future of Anchors
• Reliance on software for anchor design • Many new post-installed anchors • Confusion among engineers, contractors and building officials • Lengthy transition period
46
The Future of Anchors
• What changes will the IBC 2009 and ACI 318-11, Appendix D bring? – Clearer provisions for adhesives and concrete screws?
Questions
47
Presentation Topics
• •
Brief History of Anchor Design ACI 318-08, Appendix D • • • • • • •
• • • •
Design Equations Phi (Ф) Factors Interaction Equation Seismic Provisions Reinforcement to Prevent Breakout Other Issues Edge Distances, Thicknesses & Spacings
When to design per App. D IBC 2006 Adhesive Anchors and Concrete Screws The Future of Anchor Design
1
Prior to ACI 318-02
• Cast-In-Place anchors covered by: – PCI / ACI 349 – UBC / IBC codes listed allowable stress capacities for CIP bolts
Prior to ACI 318-02
• Design of Post-Installed anchors: – Individual manufacturers supplied load values based on testing – Values found in catalogs and ICBO/ICC reports – Methodology was allowable stress and assumed an uncracked and unreinforced section.
2
ACI 318-08, Appendix D
ACI 318, Appendix D
• Strength design method for anchorage to concrete (i.e. Nua ≤ ΦNn or Vua ≤ ΦVn) – Cast-In-Place (CIP) anchors – Post-Installed (PI) anchors
• Undercut anchors • Torque-controlled anchors • Deformation-controlled anchors
– PI anchors must be prequalified per ACI 355.2
3
Appendix D Design Equations & Failure Modes
• Design equations check 5 different failure modes – Steel capacity • Tension and Shear
– Concrete breakout capacity • Tension and Shear
– Pullout/Pull-through capacity • Tension only
– Concrete Pryout • Shear only
– Concrete side-face blowout • Tension and CIP only.
Appendix D Design Equations
4
Design Equations
Tension Capacities Nsa = nAse,Nfuta Ncb = ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Npn = Ψc,PNp Nsb = (160ca1√Abrg)λ√f’c Shear Capacities Vsa = n 0.6 Ase,V futa Vcbg = AVc/AVco(Ψec,VΨed,V Ψc,V Ψh,VVb) Vcpg = kcpNcbg
Steel Strength in Tension
5
Steel Strength In Tension – D.5.1
Nsa = nAse,Nfuta (Eq. D-3)
– Nsa – Nominal tensile strength of an anchor group – n – Number of anchors – Ase,N – Effective cross sectional area of anchor in tension – futa – Specific ultimate tensile strength of anchor
Concrete Breakout Strength in Tension
6
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) (Eq. D-5)
• Ncb – Concrete breakout strength in tension
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) • ANc – Projected failure area of group • ANco = 9 hef2 Projected failure area of one anchor (Eq. D-6)
7
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Modification for eccentric load Ψec,N = 1/[1+(2e’N/3hef)] (Eq. D-9) N Centroid of anchors
T3
T2
e’N
T1
Resultant tension load
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Modification for edge effects
If ca,min > 1.5hef then: Eq. D-10 Ψed,N = 1.0
ca
If ca,min < 1.5hef then: Eq. D-11 Ψed,N = 0.7 + 0.3 (ca,min / 1.5hef )
8
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,N Ψc,N Ψcp,NNb) Modification for cracking Ψc,N =1.4 for uncracked section if kc = 17 in eq. (D-7) Ψc,N per evaluation report (ER) if kc from ER used in eq. (D-7) Ψc,N =1.0 for cracked section
Concrete Breakout In Tension – D.5.2
Ncb=ANc/ANco(Ψec,NΨed,NΨc,NΨcp,NNb) Ψcp,N – Modification for Post-Installed anchors Uncracked concrete No supplemental reinf. to control splitting
If ca,min > cac then: Ψcp,N = 1.0 (Eq. D-12) If ca,min < cac then: Ψcp,N = ca,min/cac (Eq. D-13) Where cac= 2.5 hef (undercut anchors) 4 hef (wedge anchors)
9
Concrete Breakout In Tension – D.5.2
Ncbg=ANc/ANco(Ψec,NΨed,NΨc,NΨcp,NNb) • Basic concrete breakout strength • Nb=kc λ √f’c hef1.5 (Eq. D-7) – kc – Coefficient for basic concrete breakout strength
• Found in either App. D or per product ER
– λ – Modification factor for lightweight concrete – f’c – Concrete compressive strength – hef – Effective embedment depth
• Tested hef found in manufacturer’s catalog or product ER
Pullout Strength in Tension
10
Pullout Strength In Tension – D.5.3
Npn = Ψc,PNp
(Eq. D-14)
• Npn – Nominal pullout strength • Ψc,P – Modification for cracking – 1.0 for cracked – 1.4 for uncracked
• Np – Pullout strength in tension
Pullout Strength In Tension – D.5.3
Npn = Ψc,P Np
(Eq. D-14)
• Np – Pullout strength in tension • For PI anchors Np based on ACI 355.2 test results • For CIP anchors, Np based on: – Np = 8 Abrgf’c (Eq. D-15) headed bolts – Np = 0.9f’cehda (Eq. D-16) hooked bolts
11
Side-Face Blowout Strength in Tension
Side-Face Blowout Strength – D.5.4
Nsb = (160ca1√Abrg)λ√f’c (Eq. D-17) • Nsb – Side-face blowout strength (headed anchors only) • ca1 – edge distance • Abrg – Net bearing area of the head of anchor • λ – Modification factor for lightweight concrete
12
Steel Strength in Shear
Steel Strength In Shear – D.6.1
• Vsa = n Ase,V futa (eq. D-19) CIP HSA • Vsa = n 0.6 Ase,V futa (eq. D-20) – n – number of anchors – Ase,V – effective cross sectional area of a single anchor in shear – futa – specified tensile strength of anchor steel
13
Steel Strength In Shear – D.6.1
• Vsa may also be based on the results of tests performed and evaluated according to ACI 355.2
Concrete Breakout Strength in Shear
14
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,V Ψc,V Ψh,VVb) (Eq. D-22)
• Vcbg – Concrete breakout strength in shear
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) – AVc – projected concrete failure area of a group of anchors c
a1
V
ha 1.5ca1
s1
ca2
AVc
AVc = (1.5ca1 + s1 + ca2) ha
15
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) – AVco – maximum projected concrete failure area of a single anchor
V
c
a1
AVco = 4.5 ca12 (Eq. D-23)
1.5c1 1.5ca1 1.5ca1
AVco
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψec,V – Modification for eccentric load (Eq. D-26)
16
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψed,V – Modification for edge effects If ca2 > 1.5ca1 then Ψed,V = 1.0 (Eq. D-27)
V
If ca2 < 1.5ca1 then Ψed,V = 0.7 + 0.3ca2/1.5ca1
ca1
(Eq. D-28)
ca2
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V Modification factor for cracking Ψc,V = 1.4 for anchors located in a region where analysis indicates no cracking at service loads Who is currently doing this analysis?
17
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V = 1.0 for anchors in cracked concrete with no supplemental reinforcement or edge reinforcement smaller V than a #4 bar <#4
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V = 1.2 for anchors in cracked concrete with reinforcement of a #4 bar or greater between the anchor and the edge V
>#4
18
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψc,V = 1.4 for anchors in cracked concrete with reinforcement of a #4 bar or greater between the anchor and the edge, and with the reinforcement enclosed V within stirrups spaced at not more than 4”.
≥#4 #4@4”
Concrete Breakout In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) Ψh,V – Modification factor for shear strength of anchors located in concrete members with ha < 1.5ca1
c
When ha < 1.5ca1, AVc is reduced. However, breakout strength is not directly proportional to member thickness. Ψh,V adjusts for this.
a1
Ψh,V = √1.5ca1/ha but not less than 1.0
1.5c1
V
ha
19
Concrete Breakout Strength In Shear – D.6.2
Vcbg = AVc/AVco(Ψec,VΨed,VΨc,V Ψh,VVb) • Vb=(7(ℓe /da)0.2√da)λ√f’c (ca1)1.5
(Eq. D-24)
– ℓe – load bearing length of anchor • Same as hef if there is no sleeve on anchor • Per manufacturer if there is a sleeve
– da – outside diameter of anchor – λ – adjustment for lightweight concrete – f’c – concrete compressive strength – ca1 – edge distance
Pryout Strength in Shear
20
Concrete Pryout Strength In Shear – D.6.3
Vcpg = kcpNcbg
(Eq. D-30)
• •
kcp = 1.0 for hef < 2.5” kcp = 2.0 for hef > 2.5”
•
Ncbg – Nominal concrete breakout strength in tension – Always do tension calcs first
Phi (Ф) Factors
21
Phi (Φ) factors
• Nua ≤ ΦNn or Vua ≤ ΦVn • Phi (Ф) factors are applied to nominal capacities before comparing with factored forces • Based on: – Supplemental reinforcement – Failure mode – Load type – Anchor property
Phi (Φ) factors D.4.4 Ф Factor Failure Mode
Anchor Property
Condition A Tension
Condition B
Shear
Ductile Steel
Shear
0.75
0.65
0.65
0.60
Use Condition B Brittle
Side Face Blowout
Tension
CIP
0.75
0.75
0.70
0.70
CIP
0.75
0.75
0.70
0.70
Cat. 1
0.75
0.75
0.65
0.70
Cat. 2
0.65
0.75
0.55
0.70
Cat. 3
0.55
0.75
0.45
0.70
0.70
0.70
Breakout
CIP Cat. 1
0.65
0.70
Cat. 2
0.55
0.70
Cat. 3
0.45
0.70
CIP
0.70
0.70
Pullout
Use Condition B
Cat. 1
0.65
0.70
Cat. 2
0.55
0.70
Cat. 3
0.45
0.70
Pryout
Use Condition B
22
Supplemental Reinforcing D.4.4 • Condition A – Applies where supplementary reinforcement is present except for pullout and pryout strengths. • Condition B – Applies where supplementary reinforcement is not present, and for pullout or pryout strength.
Supplemental Reinforcing
• Supplemental Reinforcement – Reinforcement that acts to restrain the potential concrete breakout but is not designed to transfer the full design load from the anchors into the structural member. – Refer to sections D.5.2.9 and D.6.2.9 for full design load transfer requirements
23
Interaction of Tension and Shear
Interaction of Tension and Shear – D.7
24
Interaction of Tension and Shear – D.7
• If Vua≤0.2ΦVn full tension allowed – Ignore Shear
• If Nua≤0.2ΦNn full shear allowed – Ignore Tension
• Otherwise Nua + Vua ΦNn ΦVn
< 1.2
Appendix D Seismic Provisions
25
Seismic Provisions
D.3.3 – When anchor design includes earthquake forces for structures assigned to Seismic Design Category C, D, E, or F, the additional requirements of D.3.3.1 through D.3.3.6 shall apply.
D.3.3.1 – The provisions of Appendix D do not apply to the design of anchors in plastic hinge zones of concrete structures under earthquake forces.
D.3.3.2 – Post-installed structural anchors shall be qualified for use in cracked concrete and shall have passed the Simulated Seismic Tests in accordance with ACI 355.2. Pullout strength Np and steel strength of the anchor in shear Vsa shall be based on the results of the ACI 355.2 Simulated Seismic Tests.
Seismic Provisions D.3.3.3 – The anchor design strength associated with concrete failure modes shall be taken as 0.75φNn and 0.75φVn, where φ is given in D.4.4 or D.4.5, and Nn and Vn are determined in accordance with D.5.2, D.5.3, D.5.4, D.6.2, and D.6.3, assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked.
• 0.75 reduction to concrete capacity in Seismic Design Category C – F • Impractical to prove concrete remains uncracked
26
Seismic Provisions
D.3.3.4 – Anchors shall be designed to be governed by the steel strength of a ductile steel element as determined in accordance with D.5.1 and D.6.1, unless either D.3.3.5 or D.3.3.6 is satisfied. D.3.3.5 – Instead of D.3.3.4, the attachment that the anchor is connecting to the structure shall be designed so that the attachment will undergo ductile yielding at a force level corresponding to anchor forces no greater than the design strength of anchors specified in D.3.3.3. D.3.3.6 – As an alternative to D.3.3.4 and D.3.3.5, it shall be permitted to take the design strength of the anchors as 0.4 times the design strength determined in accordance with D.3.3.3. For the anchors of stud bearing walls, it shall be permitted to take the design strength of the anchors as 0.5 times the design strength determined in accordance with D.3.3.3.
Seismic Provisions
• Summary – Seismic Design Category C, D, E & F – No anchors in plastic hinge – PI anchors must pass Simulated Seismic Test – Design strength reduced by 25% – Ductile steel failure of anchors shall control, or... – Ductile yielding of attachment, or... – Anchor capacity reduced by 60%
27
Seismic Provisions
• Seismic and edge effects – At small edge distances, concrete breakout (non ductile failure mode) will often control – If attachment will not experience ductile yielding before breakout occurs, then 40% anchor capacity reduction unless... – Reinforce section to prevent breakout from occurring
Reinforcement to Prevent Concrete Breakout
28
Reinforcement to Prevent Concrete Breakout D.4.2.1 – The effect of reinforcement provided to restrain the concrete breakout shall be permitted to be included in the design models used to satisfy D.4.2. Where anchor reinforcement is provided in accordance with D.5.2.9 and D.6.2.9, calculation of the concrete breakout strength in accordance with D.5.2 and D.6.2 is not required.
D.5.2.9 – Where anchor reinforcement is developed in accordance with Chapter 12 on both sides of the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining φNn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
Reinforcement to Prevent Concrete Breakout
• Refer to Commentary RD.5.2.9 for more information
29
Reinforcement to Prevent Concrete Breakout D.6.2.9 – Where anchor reinforcement is either developed in accordance with Chapter 12 on both sides of the breakout surface, or encloses the anchor and is developed beyond the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining φVn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.
Plan
Section
• Refer to Commentary RD.6.2.9 for more info
Bars effective as anchor reinforcement
Reinforcement to Prevent Concrete Breakout
Edge Reinforcement Anchor Reinforcement
Section
Plan
• Refer to Commentary RD.6.2.9 for more info
30
Reinforcement to Prevent Concrete Breakout
• Per Commentary RD.5.2.9 and RD.6.2.9: – “As a practical matter, use of anchor reinforcement is generally limited to cast-in-place anchors.”
• What about post-installed anchors? – At small edge distances, anchor capacity will be greatly reduced for seismic design.
Other Appendix D Issues
31
Capacity Adjustments • PI anchor pullout capacity – Tested values of Np are done in 2500 psi concrete – Pullout capacities increase for higher f’c – Adjustment equations in ER
• Grout pads – 20% reduction in shear strength (D.6.1.3) – App. D makes no mention to grout pad thickness
• Shear load parallel to concrete edge – Breakout capacity doubled per D.6.2.1(c).
Triple Edge Conditions
D.5.2.3 – Where anchors are located less than 1.5hef from three or more edges, the value of hef used in Eq. (D-4) through (D-11) shall be the greater of ca,max/1.5 and one-third of the maximum spacing between the anchors within the group.
D.6.2.4 – Where anchors are influenced by three or more edges, the value of ca1 used in Eq. (D-23) through (D-29) shall be the greatest of ca2/1.5 in either direction, ha/1.5; and one-third of the maximum spacing between the anchors within the group.
32
Triple Edge Condition in Tension
Triple Edge Condition in Shear
33
Corner Condition D.6.2.1(d)
(d) For anchors located at a corner, the limiting nominal concrete breakout strength shall be determined for each edge, and the minimum value shall be used.
V V ca1
ca2 ca2
ca1
Shear Near an Edge D.6.2.1 Where anchors are located at varying distances from the edge and the anchors are welded to the attachment so as to distribute the force to all anchors, it shall be permitted to evaluate the strength based on the distance to the farthest row of anchors from the edge. In this case, it shall be permitted to base the value of ca1 on the distance from the edge to the axis of the farthest anchor row that is selected as critical, and all of the shear shall be assumed to be carried by this critical anchor row alone.
Anchors welded to plate
V
0.5V
Anchors not welded to plate
0.5V
ca1 ca1
34
Shear Near an Edge D.6.2.1
• Increase ca1 without welding to plate – Slot holes closest to edge
V ca1
Required Edge Distances, Spacings, and Thicknesses
35
Section D.8
Minimum spacings and edge distances for anchors and minimum thicknesses of members shall conform to D.8.1 through D.8.6, unless supplementary reinforcement is provided to control splitting. Lesser values from product-specific tests performed in accordance with ACI 355.2 shall be permitted. D.8.1 – Unless determined in accordance with D.8.4, minimum center-to-center spacing of anchors shall be 4da for untorqued cast-in anchors, and 6da for torqued cast-in anchors and post-installed anchors. D.8.2 – Unless determined in accordance with D.8.4, minimum edge distances for cast-in headed anchors that will not be torqued shall be based on specified cover requirements for reinforcement in 7.7. For castin headed anchors that will be torqued, the minimum edge distances shall be 6da.
Section D.8
D.8.3 – Unless determined in accordance with D.8.4, minimum edge distances for post-installed anchors shall be based on the greater of specified cover requirements for reinforcement in 7.7, or minimum edge distance requirements for the products as determined by tests in accordance with ACI 355.2, and shall not be less than 2.0 times the maximum aggregate size. In the absence of product-specific ACI 355.2 test information, the minimum edge distance shall be taken as not less than: Undercut anchors..................................................6da Torque-controlled anchors.....................................8da Displacement-controlled anchors.........................10da
36
Section D.8
D.8.4 – For anchors where installation does not produce a splitting force and that will remain untorqued, if the edge distance or spacing is less than those specified in D.8.1 to D.8.3, calculations shall be performed by substituting for da a smaller value d’a that meets the requirements of D.8.1 to D.8.3. Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of d’a. D.8.5 – The value of hef for an expansion or undercut post-installed anchor shall not exceed the greater of 2/3 of the member thickness and the member thickness minus 4 in.
Section D.8
D.8.6 – Unless determined from tension tests in accordance with ACI 355.2, the critical edge distance, cac, shall not be taken less than: Undercut anchors...............................................2.5hef Torque-controlled anchors....................................4hef Displacement-controlled anchors..........................4hef
37
Limitations of Appendix D
• Applies for CIP and some PostInstalled anchors – Specialty inserts, through bolts, adhesive anchors, screw anchors, PAT fasteners outside scope of Appendix D – ACI Commentary: “Adhesive anchors are widely used and can perform adequately. At this time…outside the scope.”
Limitations of Appendix D
• NW Concrete and LW Concrete only – Reductions in capacity in LW – CMU and Concrete on metal deck outside scope of App. D • Grouted CMU will still use existing postinstalled anchor products
38
Limitations of Appendix D
• Limits to: – Diameter (≤2”) – Embedment depth (≤25”) – Concrete compressive strength (≤8000 psi PI; <10000 psi CIP).
When to Use Appendix D
39
When to use Appendix D
• Per ACI 318-08, D.2.1 – “…anchors in concrete used to transmit structural loads by means of tension, shear, or a combination of tension and shear between (a) connected structural elements; or (b) safety-related attachments and structural elements.” – What is a “safety-related attachment”?
When to use Appendix D
• Per ACI 318-08, RD.2.1 – Commentary lists examples for safetyrelated attachments. – “…safety-related attachments that are not part of the structure (such as sprinkler systems, heavy suspended pipes, or barrier rails) are attached to structural elements.” – Will sprinkler systems be attached with cracked concrete anchors?
40
When to Use Appendix D IBC 2006
IBC 2006, Section 1911
Anchorage To Concrete – Allowable Stress Design 1911.1 Scope. The provisions of this section shall govern the allowable stress design of headed bolts, and headed stud anchors cast in normal-weight concrete for purposes of transmitting structural loads from one connected element to the other. These provisions do not apply to anchors installed in hardened concrete or where load combinations include earthquake loads or effects. The bearing area of headed anchors shall be not less than one and one-half times the shank area. Where strength design is used, or where load combinations include earthquake loads or effects, the design strength of anchors shall be determined in accordance with Section 1912. Bolts shall conform to ASTM A 307 or an approved equivalent.
41
IBC 2006, Section 1912 Anchorage To Concrete – Strength Design 1912.1 Scope. The provisions of this section shall govern the strength design of anchors installed in concrete for purposes of transmitting structural loads from one connected element to the other. Headed bolts, headed studs and hooked (J- or L-) bolts cast in concrete and expansion anchors and undercut anchors installed in hardened concrete shall be designed in accordance with Appendix D of ACI 318 as modified by Section 1908.1.16, provided they are within the scope of Appendix D. Exception: Where the basic concrete breakout strength in tension of a single anchor, Nb, is determined in accordance with Equation (D-7), the concrete breakout strength requirements of Section D.4.2.2 shall be considered satisfied by the design procedures of Sections D.5.2 and D.6.2 for anchors exceeding 2 inches (51mm) in diameter or 25 inches (635mm) tensile embedment depth. The strength design of anchors that are not within the scope of Appendix D of ACI 318, and as amended above, shall be in accordance with an approved procedure.
IBC 2006, Section 1908 Modifications to ACI 318 1908.1.16 ACI 318, Section D.3.3. Modify ACI 318, section D.3.3.2 through C.3.3.5, to read as follows: D.3.3.2 – In structures assigned to Seismic Design Category C, D, E or F, post-installed anchors for use under D.2.3 shall have passed the Simulated Seismic Tests of ACI 355.2. D.3.3.3 – In structures assigned to Seismic Design Category C, D, E or F, the design strength of anchors shall be taken as 0.75φNn and 0.75φVn, where φ is given in D.4.4 or D.4.5, and Nn and Vn are determined in accordance with D.4.1. D.3.3.4 – In structures assigned to Seismic Design Category C, D, E or F, anchors shall be designed to be governed by tensile or shear strength of a ductile steel element, unless D.3.3.5 is satisfied. D.3.3.5 – Instead of D.3.3.4, the attachment that the anchor is connecting to the structure shall be designed so that the attachment will undergo ductile yielding at a load level corresponding to anchor forces no greater than the design strength of anchors specified in D.3.3.3, or the minimum design strength of the anchors shall be at least 2.5 times the factored forces transmitted by the attachment.
42
Adhesive Anchors and Concrete Screws
Adhesives Anchors and Concrete Screws
• IBC 2006, Section 1912 – “The strength design of anchors that do not within the scope of Appendix D of ACI 318…shall be in accordance with an approved design procedure.”
• What design procedures are approved? • Who decides?
43
Adhesives Anchors and Concrete Screws
• IBC 2006, Section 104.11 104.11 Alternative materials, design and methods of construction and equipment. The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. 104.11.1 Research reports. Supporting data, where necessary to assist in the approval of materials or assemblies not specifically provided for in this code, shall consist of valid research reports from approved sources.
Adhesives Anchors and Concrete Screws
• IBC 2006, Section 104.11 – The building official has the ability to approve a material if it is not specifically referenced in the code – Adhesive anchors and screw anchors fall into this category – Caution: Most building officials are still learning about strength design provisions of anchors
44
Adhesives Anchors and Concrete Screws
• Many engineers are still designing adhesive anchors and screw anchors per ASD • Strength design code reports for adhesives and screws are just starting to come online
Adhesives Anchors and Concrete Screws
• ICC ES AC 193 – Expansion anchors – Undercut anchors – Screw anchors
• ICC ES AC 308 – Adhesive anchors
45
Code Reports
The Future of Anchors
• Reliance on software for anchor design • Many new post-installed anchors • Confusion among engineers, contractors and building officials • Lengthy transition period
46
The Future of Anchors
• What changes will the IBC 2009 and ACI 318-11, Appendix D bring? – Clearer provisions for adhesives and concrete screws?
Questions
47
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